As conventional apparatus for determining the laser welding quality of a welding section, there has been known a molten pool visualization apparatus disclosed in Patent Document 1, for example.
The molten pool visualization apparatus is equipped with a light source, a camera, and a wavelength filter. The light source emits high-luminance short-pulse laser light onto a molten pool created during laser welding. The camera has a high-speed shutter and acquires an image of the molten pool and its surrounding region. The wavelength filter is attached to the camera and transmits only the wavelength of the short-pulse laser light therethrough.
In the molten pool visualization apparatus, the light source irradiates the molten pool with the short-pulse laser light having higher luminance than plasma light or laser scattered light. The camera of the molten pool visualization apparatus is configured to open and close the high-speed shutter at intervals synchronized with the intervals at which the emission of the short-pulse laser light from the light source is started and stopped. When the high-speed shutter is opened in synchronism with the emission of the short-pulse laser light from the light source, the molten pool is photographed. At this time, the plasma light and the laser scattered light are attenuated by the wavelength filter, so that the molten pool can be observed on the monitor.